JP2018127391A - APPARATUS FOR PRODUCING SINGLE CRYSTAL OF COMPOUND, METHOD FOR PRODUCING SINGLE CRYSTAL OF COMPOUND, AND GaN SINGLE CRYSTAL - Google Patents

Abstract

To provide a compound single crystal manufacturing apparatus, a compound single crystal manufacturing method, and a GaN single crystal capable of growing a compound single crystal using a metal-containing gas and a reactive gas. A compound single crystal manufacturing apparatus includes a crystal growth unit for holding a seed crystal, a gas supply unit for supplying a metal-containing gas and a reaction gas toward the seed crystal, a seed, A heating unit 60 for heating the crystal 22 and the metal source 50 is provided. The gas supply unit 40 includes a crucible 42 that holds the metal source 50, a carrier gas supply device, and a reaction gas supply device. A porous baffle plate 48 is provided in the opening of the crucible 42. The perforated baffle plate 48 satisfies the relationship of 80% ≦ (1−VH / VB) × 100 <100% and 0.0003 <a2 / L <1.1. Where VB is the apparent volume of the porous baffle plate 48, VH is the total volume of holes contained in the porous baffle plate 48, a is the diameter of the hole, and L is the length of the hole. [Selection] Figure 1

Description

  The present invention relates to a compound single crystal manufacturing apparatus, a compound single crystal manufacturing method, and a GaN single crystal. More specifically, the present invention relates to a seed crystal surface using a metal-containing gas (a gas containing a metal vapor) and a reaction gas. The present invention relates to a compound single crystal production apparatus for growing a single crystal made of an inorganic compound, a method for producing a compound single crystal using the same, and a GaN single crystal obtained by such a method.

  Bulk single crystals made of inorganic compounds (GaAs, InP, oxides, etc.) are often produced industrially by solidification from a coincident melt (Czochralski method, Bridgman method, etc.). However, not all inorganic compounds have a congruent melt within an industrially realistic temperature and pressure range. In such a case, a flux method or a vapor phase growth method is used.

  A compound single crystal is composed of two or more elements. The vapor phase growth of the compound single crystal is realized by supplying gas species containing each element to the seed crystal surface (or the growth crystal surface) and reacting them on the surface. In this case, a halide, an organometallic compound, or the like is often used as a gas species containing the target element. However, these gas species increase the device cost due to safety concerns, and the raw material cost itself is high, which increases the production cost of the compound single crystal.

  In order to solve this problem, a gas is generated by evaporation of molten metal or sublimation or decomposition of an inorganic compound, and the resulting metal vapor or sublimation gas and reaction gas are reacted on the surface of the seed crystal, thereby producing a seed. A method of growing a single crystal or polycrystal of an inorganic compound on the surface of a crystal (hereinafter referred to as “sublimation method”) has been proposed.

For example, Non-Patent Document 1 discloses a method of growing a GaN crystal on a substrate surface using a sublimation sandwich technique.
Non-Patent Document 2 discloses a method of growing a GaN single crystal on a substrate surface by sublimating a cold-formed GaN pellet or evaporating Ga metal in an ammonia atmosphere.

Non-Patent Document 3 discloses a method of growing a GaN single crystal on a substrate surface using a gallium hydride vapor phase epitaxy (GaH-VPE) method.
Non-Patent Document 4 discloses a method of growing a thick GaN polycrystalline film on a substrate surface using a sublimation method in a nitrogen atmosphere.
Further, Non-Patent Document 5 discloses a method (growth rate: 1.6 to 7.2 μm / h) of growing a GaN single crystal on the substrate surface using a sublimation method.

In the sublimation method, as a metal source, a liquid or solid metal (eg, Al, Ga, Zn, In, Cd, Hg, Si, Ge, Sn, Mg, Mn, Cu, Ag, etc.) or a metal compound is used as a metal source. Used. The reactive gas may be a hydride gas (for example, H ₂ O, hydrocarbon gas, NH ₃ , H ₂ S, H ₂ Se, H ₂ Te, PH ₃ , AsH ₃ ) or diatomic molecular gas ( For example, O ₂ and N ₂ are used.

  Since many of these metal sources and reaction gases are relatively easy to handle and inexpensive, the production cost of a compound single crystal can be reduced by using this type of raw material. However, there are few examples in which a bulk single crystal can be stably grown with this kind of raw material combination.

P. G. Baranov et al., MRS intenet J. Nitride Semicond. Res., Vol. 3 (1998) 50 C. M. Balkas et al., J. Cryst. Growth, Vol. 208 (2000) pp. 100-106 M. Imade et al., Jpn. J. Appl. Phys., Vol. 45 (2006) pp. L878-L880 H.-J. Rost et al., Phys. Stat. Sol., Vol. 4 (2007) pp. 2219-2222 G. Lukin et al., Pys. Status Solidi C 11, No. 3-4, 491-494 (2014)

The problem to be solved by the present invention is a compound single crystal manufacturing apparatus capable of growing a single crystal made of an inorganic compound on the surface of a seed crystal over a long period of time using a metal-containing gas and a reactive gas. It is to provide.
Another problem to be solved by the present invention is to provide a compound single crystal production apparatus capable of reducing the production cost of the compound single crystal and increasing the crystal size.
Another problem to be solved by the present invention is to provide a method for producing a compound single crystal using such a compound single crystal production apparatus.
Furthermore, another problem to be solved by the present invention is to provide a GaN single crystal having a lower impurity concentration than conventional ones.

In order to solve the above-mentioned problems, a gist of a compound single crystal production apparatus according to the present invention is as follows.
(1) The compound single crystal production apparatus comprises:
A crystal growth section having a susceptor for holding a seed crystal;
A gas supply unit for supplying a metal-containing gas (a gas containing a metal vapor) generated from a metal source and a reaction gas that reacts with the gas to generate an inorganic compound toward the seed crystal;
A heating unit including a heating device for heating the seed crystal and the metal source.
(2) The gas supply unit
A crucible for holding the metal source, spaced apart from the susceptor;
A carrier gas supply device for supplying a carrier gas into the crucible and supplying a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal;
A reaction gas supply device for supplying the reaction gas toward the seed crystal;
It has.
(3) A porous baffle plate is provided at the opening of the crucible.
(4) The porous baffle plate satisfies the relationship of the following formulas (1) and (2).
80% ≦ (1-V _H / V _B ) × 100 <100% (1)
0.0003 <a ² /L<1.1 (2)
However,
V _B is the apparent volume of the perforated baffle plate,
V _H is the total volume of holes contained in the perforated baffle plate.
a is the diameter of the hole,
L is the length of the hole.

The crucible preferably has a relative density of 99% or more or an average pore diameter of 100 μm or more.
The crucible is
(A) an inner crucible for holding the metal source, and an outer crucible for accommodating the inner crucible,
(B) Between the outer wall surface of the inner crucible and the inner wall surface of the outer crucible, a carrier gas flow path is provided for flowing a carrier gas toward the inside of the inner crucible.
(C) It is preferable that the bottom or side surface of the outer crucible is provided with a carrier gas introduction hole for introducing the carrier gas into the carrier gas channel.

The crucible is a laminated crucible stacked in the order of the first crucible, the second crucible,..., The nth crucible (n ≧ 2) from the bottom to the top, and the kth crucible (1 ≦ k ≦ n−). 1) the opening and the carrier gas introduction hole of the (k + 1) th crucible are connected,
The perforated baffle plate may be provided at least in the opening of the nth crucible at the top.

The first method for producing a compound single crystal according to the present invention comprises using the compound single crystal production apparatus according to the present invention, under the condition that the temperature of each part satisfies the following formula (10), The gist is to grow a single crystal made of the inorganic compound.
T _G <T _D <T _S <T _B (10)
However,
_TG is the growth temperature,
T _S is the temperature of the metal source,
T _D is the decomposition temperature of the inorganic compound,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the crucible.

The second method for producing a compound single crystal according to the present invention uses the compound single crystal production apparatus according to the present invention, and under the condition that the temperature of each part satisfies the following formulas (11) and (12): The gist is to grow a single crystal made of the inorganic compound on the surface of the seed crystal.
T _G <T _D ≦ T _Dmax <T _Sn <T _B (11)
T _Sk ≦ T _{Sk + 1} (1 ≦ k ≦ n−1) (12)
However,
_TG is the growth temperature,
T _Sn is the temperature of the nth metal source filled in the nth crucible,
T _D is the decomposition temperature of the inorganic compound,
_TDmax is the maximum value of the decomposition temperature of the inorganic compound produced from any one or more metal elements contained in the first metal source to the nth metal source and the reaction gas,
T _Sk is the temperature of the kth metal source filled in the kth crucible,
T _{Sk + 1} is the temperature of the (k + 1) th metal source filled in the (k + 1) crucible,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the n-th crucible.

Furthermore, the GaN single crystal according to the present invention has a C impurity amount of less than 8 × 10 ¹⁵ cm ⁻³ , an H impurity amount of less than 3 × 10 ¹⁶ cm ⁻³ , and an O impurity amount of 6 × 10 6. It is summarized as being less than ¹⁵ cm ⁻³ .

In order to achieve good crystal growth using the sublimation method, the metal vapor or sublimation gas reaches the growth surface in an atomic or molecular form, and the metal vapor or sublimation gas and the reaction gas react on the growth surface. It is necessary to make it. However, it is generally difficult to stably grow a bulk single crystal by such a method. this is,
(A) generating a compound powder in the gas phase by a gas phase reaction;
(B) the metal liquefies or solidifies in the gas phase, on the surface of the grown crystal, or on other structural members;
(C) Since the reactive gas reacts directly with the metal source in the crucible and forms a passive film on the surface of the metal source, or a sudden reaction occurs due to a sudden reaction, the supply of metal vapor or sublimation gas Becoming unstable,
This is considered to be the main cause.

On the other hand, when crystal growth is performed using the sublimation method, when a porous baffle plate is provided in the opening of the crucible filled with the metal source and a carrier gas is flowed into the crucible, the mixed gas is discharged from the crucible. At the same time, the backflow of the reaction gas into the crucible is suppressed. For this reason, the supply of the metal-containing gas is stabilized.
Further, in the case of growing a single crystal, when the temperature of each part is optimized, generation of compound powder in the gas phase and liquefaction or solidification of metal at an unintended site can be suppressed. Therefore, it is possible to reduce the manufacturing cost of the compound single crystal and increase the crystal size.

  Furthermore, if the shape of the porous baffle plate is optimized, crystals can be stably grown even when the outlet gas flow rate is less than 20 m / sec. Further, when the relative density or average pore diameter of the crucible is optimized, the liquid metal can be prevented from scooping up the crucible wall surface when the liquid metal is used as the metal source. When such an apparatus is used, a GaN single crystal having an extremely low concentration of C, H, and O impurities can be obtained.

It is a cross-sectional schematic diagram of the compound single crystal manufacturing apparatus which concerns on the 1st Embodiment of this invention. It is a cross-sectional schematic diagram for demonstrating the positional relationship of a susceptor and a crucible. It is a cross-sectional schematic diagram for demonstrating the positional relationship of a crucible and RF coil. It is a cross-sectional schematic diagram of the compound single crystal manufacturing apparatus which concerns on the 2nd Embodiment of this invention.

It is a cross-sectional schematic diagram for demonstrating HVPE (Hydride Vapor Phase Epitaxy) method. It is a cross-sectional schematic diagram for demonstrating the conventional sublimation method. It is a figure which shows the average pore diameter dependence of Ga climbing height. It is a diagram showing the relationship between the diameter and the volume ratio of the porous baffle plate _{(1-V H / V B} ) × 100. It is a figure which shows the carrier gas flow rate dependence of the GaN growth rate. It is a diagram showing the a ² / L dependence of the crucible outlet gas flow rates. It is a figure which shows S _B / S _L ratio dependence of the normalization growth rate. It is a figure which shows an example of the hole structure of a porous baffle board.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Compound single crystal production equipment (1)]
In FIG. 1, the cross-sectional schematic diagram of the compound single crystal manufacturing apparatus which concerns on the 1st Embodiment of this invention is shown. In FIG. 1, the compound single crystal manufacturing apparatus 10 has the following configuration.
(1) The compound single crystal manufacturing apparatus 10
A crystal growth unit 20 including a susceptor 24 for holding a seed crystal 22;
A gas supply unit 40 for supplying a metal-containing gas (a gas containing a metal vapor) generated from the metal source 50 and a reaction gas that reacts therewith to generate an inorganic compound toward the seed crystal 22;
And a heating unit 60 including a heating device 62 for heating the seed crystal 22 and the metal source 50.
(2) The gas supply unit 40
A crucible 42 for holding the metal source 50, spaced apart from the susceptor 24;
A carrier gas supply device for supplying a carrier gas into the crucible 42 and supplying a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal 22;
A reaction gas supply device for supplying the reaction gas toward the seed crystal 22;
It has.
(3) A porous baffle plate 48 is provided at the opening of the crucible 42.

The compound single crystal manufacturing apparatus 10 is
(A) a first movable device 28 for changing a vertical distance or a horizontal distance between the perforated baffle plate 48 and the susceptor 24;
(B) a second movable device 64 for changing the vertical distance or horizontal distance between the heating device 62 and the crucible 42, and / or
(C) Angle changing device 30 for changing the tilt angle of the surface of seed crystal 22
May be further provided.

[1.1. Crystal growth part]
[1.1.1. Susceptor]
The crystal growth unit 20 includes a susceptor 24 for holding the seed crystal 22. The susceptor 24 is installed in the reaction vessel 26. The atmosphere and pressure can be controlled in the reaction vessel 26 by using an exhaust device (not shown).
The structure of the susceptor 24 is not particularly limited, and an optimal structure can be selected according to the purpose. Moreover, the material of the reaction vessel 26 is not particularly limited, and an optimum material can be selected according to the purpose. An example of the reaction vessel 26 is a quartz chamber.

The susceptor 24 is installed at a position where the mixed gas discharged through the perforated baffle plate 48 can be supplied to the surface of the seed crystal 22. The positional relationship between the susceptor 24 and the crucible 42 is not particularly limited, and an optimal positional relationship can be selected according to the structure of the crucible 42.
In the example shown in FIG. 1, the susceptor 24 is disposed above the crucible 42. The mixed gas discharged through the perforated baffle plate 48 rises toward the susceptor 24.
On the other hand, although not shown, when the device further includes a means for changing the flow of the mixed gas discharged from the crucible 42 in the horizontal direction, the susceptor 24 and the crucible 42 can be arranged in the horizontal direction.

That is, the present invention
(A) A vertical furnace in which the reaction vessel 26 is installed so that the longitudinal direction of the reaction vessel 26 is vertical, and the crucible 42 and the susceptor 24 are arranged in the vertical direction, or
(B) a horizontal furnace in which the reaction vessel 26 is installed so that the longitudinal direction of the reaction vessel 26 is horizontal, and the crucible 42 and the susceptor 24 are arranged in the horizontal direction;
It can be applied to any of these.

[1.1.2. First movable device]
The susceptor 24 (or seed crystal 22) is arranged at a predetermined distance from the perforated baffle plate 48 (or the opening of the crucible 42). The distance between the perforated baffle plate 48 and the surface of the susceptor 24 (hereinafter also referred to as “baffle-susceptor distance”) may be fixed or changeable.

  When the distance between the baffle and the susceptor is fixed, the distance between the perforated baffle plate 48 and the surface of the grown crystal (hereinafter also referred to as “baffle-grown crystal distance”) becomes shorter as the single crystal grows. . Generally, in order to stably continue the growth of a single crystal, it is preferable to maintain the distance between the baffle and the grown crystal within a predetermined range. Therefore, when growing a thick single crystal, it is preferable to include the first movable device 28 for changing the vertical distance or horizontal distance between the baffle and the susceptor.

The first movable device 28 may be provided in either the crystal growth unit 20 or the gas supply unit 40, or may be provided in both. That is, the first movable device 28 is
(A) The susceptor 24 is movable with the crucible 42 fixed.
(B) The crucible 42 can be moved with the susceptor 24 fixed, or
(C) Any of those that can move both the susceptor 24 and the crucible 42 may be used.

  In order to stably continue the growth of the single crystal, it is preferable to actively control the temperature of each part. For this purpose, the first movable device 28 is preferably capable of moving the susceptor 24. As shown in FIG. 1, in the case of a vertical furnace in which the susceptor 24 is disposed above the crucible 42, the first movable device 28 is preferably capable of moving the susceptor 24 in the vertical direction.

[1.1.3. Angle change device]
The tilt angle of the surface of the seed crystal may be fixed or may be changeable. Here, the “tilt angle of the surface of the seed crystal (hereinafter also simply referred to as“ tilt angle ”)” refers to an angle formed by the normal direction of the surface of the seed crystal 22 and the supply direction of the mixed gas.
The mixed gas is usually supplied from the normal direction of the surface of the seed crystal 22. However, if the mixed gas is supplied from the oblique direction with respect to the surface of the seed crystal 22, the growth rate may increase. In such a case, it is preferable to provide the crystal growth unit 20 with an angle changing device 30 for changing the tilt angle.

  The structure of the angle changing device 30 is not particularly limited, and an optimal structure can be selected according to the purpose. The change range of the tilt angle is not particularly limited, and an optimum angle can be selected according to the purpose. Usually, the inclination angle is 0 to 60 °.

[1.2. Gas supply unit]
The gas supply unit 40 supplies a metal-containing gas and a reaction gas that reacts with the metal-containing gas and generates an inorganic compound toward the seed crystal 22. The metal-containing gas is generated by heating the metal source 50 to a predetermined temperature.
Here, “metal-containing gas” refers to a gas containing metal vapor obtained by evaporating molten metal. The metal source 50 may be made of only a metal, or may be a mixture of a metal and a metal compound. When the metal source 50 contains an appropriate amount of a metal compound, the element contained in the metal compound can be doped into the growth crystal.

As described above, the gas supply unit 40
A crucible 42 for holding the metal source 50, spaced apart from the susceptor 24;
A carrier gas supply device for supplying a carrier gas into the crucible 42 and supplying a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal 22;
A reaction gas supply device for supplying the reaction gas toward the seed crystal 22;
It has.
A porous baffle plate 48 is provided in the opening of the crucible 42.

[1.2.1. Perforated baffle plate]
In the present invention, a porous baffle plate 48 is provided in the opening of the crucible 42. This is different from the conventional one. Here, the “perforated baffle plate” refers to a plate-like member in which a plurality of small-diameter through holes are formed. The perforated baffle plate 48 is
(A) a function of discharging the mixed gas from the inside of the crucible 42 to the outside; and
(B) It is necessary to have a function of suppressing the backflow of the reaction gas from the outside to the inside of the crucible 42. Therefore, it is preferable to select the diameter and number of the through holes so that these functions are compatible.

  In general, the smaller the opening area of the porous baffle plate 48 (= area per through hole × number of through holes), the smaller the flow rate of the mixed gas passing through the porous baffle plate 48 (hereinafter referred to as “crucible outlet gas flow rate”). (Also referred to as)), the reaction gas backflow prevention function is improved. On the other hand, if the opening area becomes too small, the resistance when the mixed gas passes through the perforated baffle plate 48 increases, so that the discharge function of the mixed gas decreases.

  Furthermore, if the crucible outlet gas flow rate is too fast, the temperature of the perforated baffle plate 48 is lowered. As a result, the temperature of the metal-containing gas passing through the perforated baffle plate 48 decreases, and metal droplets may be generated on the grown crystal. Further, the reaction gas that has flowed back may be mixed in the crucible 42 without being decomposed when passing through the perforated baffle plate 48, and may react with the metal source in the crucible 42. Therefore, it is preferable that the perforated baffle plate 48 satisfies the following conditions.

[A. Volume ratio ([1-V _H / V _B ] × 100 ratio)]
The perforated baffle plate 48 preferably satisfies the relationship of the following formula (1).
80% ≦ (1-V _H / V _B ) × 100 <100% (1)
However,
V _B is the apparent volume of the perforated baffle plate 48,
V _H is the total volume of holes contained in the perforated baffle plate 48.
The “apparent volume” refers to the volume of the porous baffle plate 48 including the porous portion.

When the volume ratio ([1-V _H / V _B ] × 100 ratio) is small (that is, when the number of holes per unit area is large), in order to prevent the reaction gas from being mixed into the crucible 42, the crucible outlet gas It is necessary to increase the flow velocity. However, as the crucible outlet gas flow rate increases, the temperature of the porous baffle plate 48 tends to decrease. In order to prevent mixing of the metal-containing gas without excessively reducing the temperature of the porous baffle plate 48, the volume ratio is preferably 80% or more. The volume ratio is preferably 85% or more.
On the other hand, when the volume ratio becomes excessively large, it becomes difficult to discharge the metal-containing gas from the crucible. Therefore, the volume ratio needs to be less than 100%. The volume ratio is preferably 95% or less.

By using the porous baffle plate 48 that satisfies the formula (1), the crucible outlet gas flow velocity can be made less than 20 m / sec. This is because the reaction gas (for example, NH ₃ ) is decomposed when passing through the holes of the porous baffle plate 48 by suppressing the temperature drop of the porous baffle plate 48, and the reactive gas is not supplied to the metal source 50. Because.

[B. a ² / L ratio]
It is preferable that the perforated baffle plate 48 further satisfies the relationship of the following formula (2) in addition to the formula (1).
0.0003 <a ² /L<1.1 (2)
However,
a is the diameter of the hole in the perforated baffle plate 48;
L is the length of the hole in the perforated baffle plate 48.

As will be described later, the crucible outlet gas flow velocity is proportional to the reciprocal of the opening area (S _p ) of the porous baffle plate 48. On the other hand, the gas conductance C of the perforated baffle plate 48 is expressed by the following equation (3).
C = π × (a / 2) ⁴ × P × n / (8 × η × L) (3)
However,
P is the process pressure (Pa),
η is the viscosity coefficient (μP) of the gas.

From the crucible outlet gas flow rate equation and the gas conductance equation, it can be seen that the crucible outlet gas flow rate does not increase as the opening area (S _p ) decreases. For example, when the opening area of the perforated baffle plate 48 becomes smaller than a certain value, the crucible outlet gas flow velocity becomes smaller due to a decrease in gas conductance (see FIG. 10). From FIG. 10, it can be seen that the range of a ² / L that satisfies the crucible outlet gas flow rate of 1 m / sec or more is expressed by the equation (2).

[C. S _B / S _L ratio (molten metal area ratio)]
As described above, it has been shown that there are optimum values for the volume ratio and the a ² / L ratio. However, the area (S _B ) of the porous baffle plate 48 also requires a certain area or more. Here, when the metal source 50 is a molten metal, the surface area (molten metal area) is S _L.

When the area S _B of the perforated baffle plate 48 is too small compared to the molten metal surface area S _L of the metal source 50, the growth rate decreases. Therefore, the ratio of the area (S _B ) of the porous baffle plate 48 to the surface area (S _L ) of the metal source 50 (= S _B / S _L ratio) is preferably 0.1 or more. The S _B / S _L ratio is preferably 0.3 or more, and more preferably 0.5 or more.
On the other hand, as described later, the case of using a double crucible, it is also possible to increase the S _B from S _L. However, there is no practical benefit also by increasing the S _B more than necessary. Therefore, the S _B / S _L ratio is preferably 2.5 or less. The S _B / S _L ratio is preferably 2.0 or less, and more preferably 1.5 or less.

[D. Hole shape]
The holes formed in the perforated baffle plate 48 may be holes having a uniform diameter (for example, a columnar shape, a prismatic shape, etc.), or have different diameters along the thickness direction of the perforated baffle plate 48. What has a location may be sufficient. If the diameter of the hole is partially reduced, the opening area is reduced and the crucible outlet gas flow rate is improved. Therefore, by changing the hole structure of the perforated baffle plate 48, the gas flow rate can be locally increased, and gas mixing becomes easy.

  FIG. 12 shows an example of the hole structure of the perforated baffle plate 48. FIG. 12A shows an example of a hole having a uniform diameter along the thickness direction. FIG. 12B is an example of a hole having a diameter that is inversely tapered from the metal source 50 toward the seed crystal 22. FIG. 12C is an example of a hole whose diameter decreases in a curve from the metal source 50 toward the seed crystal 22. 12D and 12E are examples of holes each having a diameter that is narrowed in the middle.

On the other hand, FIG. 12F is an example of a hole whose diameter increases in a tapered shape from the metal source 50 toward the seed crystal 22. Even in such a structure, the gas that has passed through the perforated baffle plate 48 spreads in the in-plane direction, so that gas mixing is facilitated. Such an effect can also be realized with a structure as shown in FIGS. Furthermore, even if the diameter is constant, by adopting the structure as shown in FIG. 12 (i), the diffusion of gas in the in-plane direction can be promoted as in FIGS. 12 (f) to 12 (h). it can. As a result, the formation of polycrystals and particles on the porous baffle plate 48 is suppressed, and the quality of the grown crystal is improved.
FIGS. 12 (j) and 12 (k) are examples in which conical or columnar protrusions are formed on the upper surface of the porous baffle plate 48. On the other hand, FIG. 12 (l) shows an example of a hole in which a protrusion is formed in the middle of the hole and the diameter is narrowed in the middle.

[1.2.2. Crucible]
[A. Crucible structure]
The structure of the crucible 42 is not particularly limited as long as it has the functions described above. In the example shown in FIG.
(A) an inner crucible 42a for holding the metal source 50 and an outer crucible 42b for accommodating the inner crucible 42a;
(B) A carrier gas flow path 42c is provided between the outer wall surface of the inner crucible 42a and the inner wall surface of the outer crucible 42b for flowing the carrier gas toward the inside of the inner crucible 42a.
(C) A carrier gas introduction hole 42d for introducing a carrier gas into the carrier gas channel 42c is provided on the bottom or side surface of the outer crucible 42b.
In the example shown in FIG. 1, the carrier gas introduction hole 42d is provided on the bottom surface of the outer crucible 42b, but can also be provided on the side surface of the outer crucible 42b.

  The carrier gas flow path 42c only needs to be capable of flowing the carrier gas toward the inside of the inner crucible 42a. However, if the flow of the carrier gas inside the inner crucible 42a is far away from the surface of the metal source 50, the discharge amount of the metal-containing gas decreases. Therefore, it is preferable that the carrier gas flow path 42 c be capable of flowing a carrier gas toward the surface of the metal source 50, or be capable of flowing the carrier gas along the vicinity of the surface of the metal source 50.

  In order to increase the discharge amount of the metal-containing gas without complicating the structure of the crucible 42, the carrier gas channel 42c is configured to allow the carrier gas to flow toward the tip of the inner crucible 42a. In addition, a carrier gas flow direction adjuster 42e for changing the flow of the carrier gas reaching the tip of the inner crucible 42a to a direction toward the metal source 50 is preferably provided on the upper portion of the outer crucible 42b. .

  When the shape of the carrier gas channel 42c formed in the gap between the inner crucible 42a and the outer crucible 42b is optimized, the carrier gas can flow toward the tip of the inner crucible 42a. The carrier gas flow direction adjuster 42e only needs to be capable of changing the upward carrier gas flow reaching the tip of the inner crucible 42a downward or obliquely downward.

  For example, as shown in FIG. 1, when a cylindrical member (carrier gas flow direction adjuster 42e) having an outer diameter smaller than the inner diameter of the inner crucible 42a is provided at the tip of the outer crucible 42b, a vertically upward carrier gas flow is generated. Can be changed vertically downward. The carrier gas whose flow direction is changed vertically downward is sprayed on the surface of the metal source 50 to become a mixed gas containing a metal-containing gas. The carrier gas (mixed gas) that has collided with the surface of the metal source 50 is again changed in the direction of the flow upward in the vertical direction, and is discharged to the outside through the perforated baffle plate 48.

[B. Crucible materials]
The material of the crucible 42 is not particularly limited, and an optimum material can be selected according to the type of the metal source 50.
Examples of the material for the crucible 42 include graphite, SiC-coated graphite, pBN-coated graphite, and TaC-coated graphite.

[C. Relative density and average pore size]
When the metal source 50 is a liquid metal and the metal source 50 has good wettability to the surface of the inner crucible 42a, the liquid metal may creep up the wall surface of the inner crucible 42a during crystal growth. . If this creeping occurs during crystal growth, the supply of raw material to the surface of the seed crystal 22 becomes unstable. Further, depending on conditions, the liquid metal may get over the side wall of the inner crucible 42a, and the liquid metal may leak out of the inner crucible 42a. Therefore, the creeping up causes an increase in the impurity concentration in the grown crystal. In the case of using a liquid metal as the metal source 50, it is preferable to suppress creeping in order to obtain a growth crystal with few impurities.

As a method of suppressing creeping, there are (a) a method of increasing the relative density of the inner crucible 42a and (b) a method of increasing the average pore diameter of the inner crucible 42a.
The former is a method of suppressing creeping itself due to capillary action by eliminating pores. In order to suppress creeping up, the inner crucible 42a preferably has a relative density of 99% or more.

In the latter case, when the inner crucible 42a is porous (that is, when it is difficult to densify the inner crucible 42a due to various restrictions), the creeping height is lowered by increasing the average pore diameter. It is a method to do.
The scooping height h is expressed by the following formula (4).
h = 2γ _L cos θ / ρgr (4)
Here, θ is the contact angle, γ _L is the surface tension of the molten metal, r is the inner diameter of the tube (pore), ρ is the density of the molten metal, and g is the gravitational acceleration.

Of these, the surface tension γ _L and the density ρ are determined by the molten metal. On the other hand, the contact angle θ is determined by the interfacial tension between the molten metal and the inner crucible 42a, and the inner diameter r of the tube is determined by the surface of the inner crucible 42a and the internal pore structure. Therefore, the scooping height h is determined according to the equation (4), and when the height is higher than the depth of the inner crucible 42a, the liquid metal leaks outside the inner crucible 42a. Therefore, it is preferable to use a material that does not easily cause such a phenomenon for the inner crucible 42a. In order to make the height of creeping up to several cm or less, the average pore diameter is preferably 100 μm or more (see FIG. 7).
It should be noted that the condition that the relative density is 99% or more or the average pore diameter is 100 μm or more is sufficient as long as the inner crucible 42a is satisfied, but the outer crucible 42b may be further satisfied.

[1.2.3. Carrier gas supply device]
The carrier gas supply device supplies the carrier gas into the crucible 42 and supplies a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal 22. The structure of the carrier gas supply device is not particularly limited, and an optimal structure can be selected according to the purpose. In the example shown in FIG. 1, the carrier gas supply device includes a pipe 44 for flowing a carrier gas, one end of which is connected to the carrier gas introduction hole 42 d of the outer crucible 42 b and the other end is a carrier gas supply source ( (Not shown).

[1.2.4. Reaction gas supply device]
The reactive gas supply device is for supplying the reactive gas toward the seed crystal 22. The reaction gas supply device may supply only the reaction gas, or may supply a mixture of the reaction gas and the dilution gas (carrier gas).

  In order to grow a single crystal made of an inorganic compound on the surface of the seed crystal 22, it is necessary that the metal-containing gas and the reaction gas are uniformly mixed in the vicinity of the surface of the seed crystal 22. The reactive gas supply device is not particularly limited as long as it has such a function. In the example shown in FIG. 1, the reaction gas supply device includes a pipe 46 for supplying a reaction gas, one end of which is inserted into the reaction vessel 26 and the other end is a reaction gas supply source (not shown). And a dilution gas supply source (not shown).

  The reaction gas supply device is preferably capable of supplying the reaction gas toward the mixed gas discharged through the perforated baffle plate 48. For this purpose, the flow direction of the reaction gas is changed between the susceptor 24 and the crucible 42 to the direction toward the mixed gas, and the reaction gas flow direction adjuster 52 for promoting the mixing of the mixed gas and the reaction gas. Is preferably provided.

For example, as shown in FIG. 1, when the susceptor 24 is arranged vertically above the crucible 42, a hollow disk (reactive gas flow direction adjuster 52) is inserted between the susceptor 24 and the crucible 42. In this case, the mixed gas of the metal-containing gas and the carrier gas rises toward the seed crystal 22 as it is through the through hole of the porous baffle plate 48.
On the other hand, the reaction gas introduced into the reaction vessel 26 rises in the reaction vessel 26 and collides with the lower surface of the hollow disk through the side of the crucible 42. The reaction gas that collides with the lower surface of the hollow disk is changed in the flow direction to the horizontal direction (the direction of the opening of the crucible 42), and merges with the mixed gas above the porous baffle plate 48. The combined gas (mixture of the mixed gas and the reactive gas) is supplied to the surface of the seed crystal 22 by changing the flow direction upward again at the opening of the hollow disk.

  Even if the reaction gas flow direction adjuster 52 is not provided, the reaction gas can be supplied to the surface of the seed crystal 22, but by providing the reaction gas flow direction adjuster 52, a combined gas having a uniform composition can be obtained. Can be generated. Further, since the combined gas having a uniform composition is supplied to the surface of the seed crystal 22, the growth of the single crystal is stabilized.

[1.3. Heating unit]
[1.3.1. Heating device]
The heating unit 60 includes a heating device 62 for heating the seed crystal 22 (or the susceptor 24) and the metal source 50 (or the crucible 42). The structure of the heating device 62 is not particularly limited, and an optimal structure can be selected according to the purpose.
As the heating device 62, for example,
(A) a resistance heating device that heats the seed crystal 22 and the metal source 50 using a heater;
(B) There is a high-frequency heating device that heats the seed crystal 22 and the metal source 50 using an RF coil.

Among these, the resistance heating device heats not only the seed crystal 22 and the metal source 50 but also the reaction vessel 26 that shields them from the outside air. Therefore, the resistance heating device is effective only when the growth temperature of the single crystal is lower than the heat resistance temperature of the reaction vessel 26.
On the other hand, the high-frequency heating device can directly heat the seed crystal 22 and the metal source 50 without directly heating the reaction vessel 26 by optimizing the material of the reaction vessel 26. Therefore, the high-frequency heating device is effective particularly when the growth temperature of the single crystal is higher than the heat resistance temperature of the reaction vessel 26.

The number of heating devices 62 may be one, or two or more. When a plurality of heating devices 62 are used, independent control of the temperature of each part is easy, but the structure of the device may be complicated, and it may be complicated to actively control the temperature of each part.
On the other hand, when one heating device 62 is used, the structure of the device is relatively simple, but it is difficult to actively control the temperature of each part. In this case, it is preferable to control the position between the heating device 62 and the crucible 42 using a second movable device 64 described later.

[1.3.2. Second movable device]
The heating device 62 is disposed outside the reaction vessel 26 and around the seed crystal 22 and the crucible 42. The distance between the heating device 62 and the crucible 42 (hereinafter referred to as “distance between the heating device and the crucible”) may be fixed, or may be changeable.
Here, “distance between heating device and crucible”
(A) In the case of a vertical furnace as shown in FIG. 1, the vertical reference point of the heating device 62 (for example, the lower end of the RF coil whose central axis is arranged in the vertical direction) and the vertical of the crucible 42. A distance (vertical distance) from a direction reference point (eg, the surface of the metal source 50 in the crucible 42);
(B) Although not shown, in the case of a horizontal furnace, the horizontal reference point of the heating device 62 (for example, one end of the RF coil whose central axis is arranged in the horizontal direction) and the horizontal reference point of the crucible 42 are shown. Distance (horizontal distance) between points (for example, central axis of crucible 42)
Say.

  When the distance between the heating device and the crucible is fixed, the temperature of each part may deviate from the optimum value as the single crystal grows, and it may be difficult to continue the growth. Therefore, when growing a thick single crystal, it is preferable to include the second movable device 64 for changing the vertical distance or the horizontal distance between the heating device and the crucible.

The 2nd movable device 64 may be provided in any one of the heating part 60 or the gas supply part 40, or may be provided in both. That is, the second movable device 64 is
(A) A device capable of moving the heating device 62 with the crucible 42 fixed.
(B) The crucible 42 can be moved with the heating device 62 fixed, or
(C) Any of those that can move both the heating device 62 and the crucible 42 may be used.

  In order to stably continue the growth of the single crystal, it is preferable to actively control the temperature of each part. For this purpose, the second movable device 64 is preferably capable of moving the heating device 62. For example, as shown in FIG. 1, when the reaction vessel 26 is arranged so that the longitudinal direction of the reaction vessel 26 is vertical, the second movable device 64 can move the heating device 62 in the vertical direction. preferable.

[1.4. Control unit]
The compound single crystal manufacturing apparatus 10 includes a control unit (not shown) for controlling the temperature of the susceptor 24 (or the grown crystal), the temperature of the crucible 42, the carrier gas flow rate, the reaction gas flow rate, and the like. When the compound single crystal manufacturing apparatus 10 includes the first movable device 28, the second movable device 64, or the angle changing device 30, the control unit also controls these operations.

[1.4.1. Temperature and pressure control]
The crucible 42 including the metal source 50 and the susceptor 24 holding the seed crystal 22 are heated by the heating device 62. Temperature of metal source 50 (or temperature of inner crucible 42a): T _S , growth temperature (temperature of growth crystal or seed crystal 22 or susceptor 24): T _G , and temperature of perforated baffle plate 48: T _B Is monitored by a radiation thermometer or thermocouple. These temperatures can be controlled by applying feedback to the power applied to the heating device 62, the position of the heating device 62, and the position of the susceptor 24.

  The growth pressure (pressure in the reaction vessel 26) is monitored by a pressure gauge (for example, a Baratron pressure gauge). The growth pressure can be controlled by the pumping speed (determined by the number of rotations of the vacuum pump and the conductance valve opening) and the gas flow rate.

[1.4.2. Control of first movable device]
FIG. 2 is a schematic sectional view for explaining the positional relationship between the susceptor 24 and the crucible 42. FIG. 2 shows an example of a vertical furnace, that is, an example in which the susceptor 24 and the crucible 42 are arranged in the vertical direction. As described above, in order to stably continue the growth of the single crystal 32, the compound single crystal manufacturing apparatus 10 preferably includes the first movable device 28 for changing the baffle-susceptor distance. .

The movable width of the susceptor 24 (or the seed crystal 22) affects the thickness of the single crystal 32 that can be manufactured. In order to obtain the thick single crystal 32, the movable width of the susceptor 24 is preferably 20 mm or more. The movable width is preferably 100 mm or more.
Moreover, it is preferable that the changing speed of the baffle-susceptor distance (driving speed of the first movable device 28) can be freely adjusted in the range of 0.1 mm / h to 5 mm / sec.

[1.4.3. Control of second movable device]
FIG. 3 is a schematic sectional view for explaining the positional relationship between the crucible 42 and the heating device (RF coil) 62. FIG. 3 shows an example of a vertical furnace in which the reaction vessel 26 is arranged so that the longitudinal direction of the reaction vessel 26 is a vertical direction. As described above, when the thick single crystal 32 is grown, it is preferable to include the second movable device 64 for changing the distance between the heating device and the crucible.

The movable width of the heating device 62 affects the quality and growth rate of the single crystal 32. In order to obtain a high quality and thick single crystal 32 in the vertical furnace, the movable width of the second movable device 62 is:
(A) The lower end position of the heating device 62 is movable downward by 20 mm or more from the upper end position of the metal source 50,
(B) The lower end position of the heating device 62 is movable upward by 10 mm or more from the upper end position of the metal source 50, and
(B) The total movable width of the lower end of the heating device 62 is preferably 50 mm or more. The total movable width of the heating device 62 is preferably 200 mm or more.
Moreover, it is preferable that the changing speed of the distance between the heating device and the crucible (driving speed of the second movable device 64) can be freely adjusted in the range of 0.1 mm / h to 5 mm / sec.

[2. Compound single crystal production equipment (2)]
In FIG. 4, the cross-sectional schematic diagram of the compound single crystal manufacturing apparatus which concerns on the 2nd Embodiment of this invention is shown. In FIG. 4, the compound single crystal manufacturing apparatus 12 has the following configuration.
(1) The compound single crystal production apparatus 12
A crystal growth unit 20 including a susceptor 24 for holding a seed crystal 22;
The first metal source 74 (1), the second metal source 74 (2),... The metal-containing gas generated from the nth metal source 74 (n) and the reaction gas that reacts with this to produce an inorganic compound A gas supply unit 40 for supplying toward the crystal 22;
And a heating unit 60 including a heating device 62 for heating the seed crystal 22 and the first metal source 74 (1), the second metal source 74 (2), ... the nth metal source 74 (n). .
(2) The gas supply unit 40
A crucible 72 for holding the first metal source 74 (1), the second metal source 74 (2),... The nth metal source 74 (n), spaced apart from the susceptor 24;
A carrier gas supply device for supplying a carrier gas into the crucible 72 and supplying a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal 22;
A reaction gas supply device for supplying the reaction gas toward the seed crystal 22;
It has.
(3) A porous baffle plate 48 is provided at the opening of the crucible 72.

The compound single crystal production apparatus 12 is
(A) a first movable device 28 for changing a vertical distance or a horizontal distance between the perforated baffle plate 48 and the susceptor 24;
(B) a second movable device 64 for changing the vertical distance or horizontal distance between the heating device 62 and the crucible 42, and / or
(C) Angle changing device 30 for changing the tilt angle of the surface of seed crystal 22
May be further provided.

[2.1. Laminated crucible and perforated baffle plate]
In the present embodiment, the crucible 72 is
A first crucible 72 (1), a second crucible 72 (2),... An nth crucible 72 (n) (n ≧ 2) in this order from the bottom to the top,
The k-th crucible 72 (k) (1 ≦ k ≦ n−1) opening is connected to the (k + 1) -th crucible 72 (k + 1) carrier gas introduction hole.
The perforated baffle plate 48 is provided at least in the opening of the nth crucible 72 (n) at the top. This point is different from the first embodiment. In FIG. 4, only the first crucible 72 (1) and the second crucible 72 (2) are shown, but this is merely an example.

  When the opening of the k-th crucible 72 (k) and the carrier gas introduction hole of the (k + 1) -th crucible 72 (k + 1) are connected, the first-th crucible 72 (1) at the bottom is connected to the n-th crucible 72 at the top. The carrier gas can be made to flow at a stretch until (n). When the carrier gas introduction hole is in the bottom surface of each k-th crucible 72 (k), such connection is facilitated.

In the laminated crucible, the perforated baffle plate 48 may be provided at the opening of each k-th crucible 72 (k) or only at the opening of the n-th crucible 72 (n) at the top. May be. Even when the porous baffle plate 48 is provided only in the opening of the n-th crucible 72 (n) at the uppermost part, the backflow of the reaction gas can be prevented.
The other points regarding the crucible (laminated crucible) 72 and the perforated baffle plate 48 are the same as those in the first embodiment, and thus the description thereof is omitted.

[2.2. Metal source]
The first crucible 72 (1), the second crucible 72 (2),..., The n th crucible 72 (n) have a first metal source 74 (1), a second metal source 74 (2),. A metal source 74 (n) is filled. In the laminated crucible, each k-th metal source 74 (k) may be the same material or a different material.

When metal vapor is generated from molten metal, the evaporation rate of the metal vapor is mainly proportional to the area of the molten metal surface. Therefore, when each k-th crucible 72 (k) is filled with the same type of molten metal, the evaporation rate of the metal vapor can be increased as compared with the case where one crucible is used.
On the other hand, when each k-th crucible 72 (k) is filled with a different metal source, a metal-containing gas containing two or more kinds of metal elements is generated, that is, two or more kinds of metal elements are formed on the surface of the seed crystal 22. A single crystal made of a multi-element inorganic compound containing can be grown.
Other points regarding the metal source are the same as those in the first embodiment, and thus the description thereof is omitted.

[2.3. First movable device]
The compound single crystal manufacturing apparatus 12 shown in FIG. 4 may include a first movable device 28 for changing the baffle-susceptor distance.
In this case, the “porous baffle plate” serving as a reference for the distance between the baffle and the susceptor refers to the porous baffle plate 48 provided in the opening of the n-th crucible 72 (n) at the top.
Since the other points regarding the first movable device 28 are the same as those of the first embodiment, description thereof will be omitted.

[2.4. Second movable device]
The compound single crystal manufacturing apparatus 12 shown in FIG. 4 may further include a second movable device 64 for changing the distance between the heating device and the crucible.
In the case of a vertical furnace, the movable width of the second movable device is
(A) The lower end position of the heating device 62 is movable downward by 20 mm or more from the upper end position of the first metal source 74 (1) filled in the first crucible 72 (1) at the lowest part,
(B) The lower end position of the heating device 62 is movable upward by 10 mm or more from the upper end position of the nth metal source 74 (n) filled in the nth crucible 72 (n) at the top, and ,
(B) It is preferable that the total movable width of the lower end of the heating device 62 is not less than the height of the crucible 72 +50 mm.
Other points regarding the second movable device are the same as those in the first embodiment, and thus the description thereof is omitted.

[2.5. Other configurations]
Other configurations relating to the compound single crystal manufacturing apparatus 12 are the same as those in the first embodiment, and thus description thereof is omitted.

[3. Compound Single Crystal Production Method (1)]
The method for producing a compound single crystal according to the first embodiment of the present invention uses the compound single crystal production apparatus 10 according to the first embodiment of the present invention to perform seed crystal 22 under a predetermined temperature condition. A single crystal 32 made of an inorganic compound is grown on the surface of the substrate.

[3.1. Metal source]
In the present invention, the type of the metal source 50 filled in the crucible 42 is not particularly limited, and an optimal one can be selected according to the purpose. In the present invention, the term “metal” includes semimetals such as Si and Ge.

As the metal source 50, a metal that is liquid or solid at room temperature can be used. Examples of such metals include B, Al, Ga, In, Zn, Cd, Hg, Si, Ge, Sn, Mg, Mn, Ti, V, Fe, Co, Ni, Cu, Y, Zr, and Nb. , Mo, Ag and the like.
In addition to these metals, the metal source 50 may contain compounds of these metals (oxides, nitrides, carbides, etc.). When the metal source 50 comprises a suitable amount of a metal compound, when heated to a decomposition temperature T _D or higher, an element other than the metal elements (e.g., oxygen) can be generated a metal-containing gas containing.

The metal used as the metal source 50 may be a pure metal, or a mixture or alloy containing two or more metals. In order to stabilize the composition of the metal-containing gas, it is preferable to use pure metal for the metal source 50.
In particular, the metal source 50 is a metal containing at least one metal element selected from the group consisting of Al, Ga, In, Zn, Cd, Hg, Si, Ge, Sn, Mg, Mn, Cu, and Ag. Is preferred. Since these can generate metal vapor at a low temperature (<1500 ° C.), they are suitable as the metal source 50. A standard for a metal that can be easily evaporated is one whose boiling point is about 2500 ° C. or less.

[3.2. Reaction gas]
The reaction gas is an element that constitutes an inorganic compound and is used to supply an element other than the element supplied from the metal source 50. In the present invention, the type of reaction gas is not particularly limited, and an optimum gas can be selected according to the purpose.

The reaction gas is preferably a gas containing at least one element selected from the group consisting of C, B, N, P, As, Sb, O, S, Se, and Te. Specifically, as a reaction gas,
(A) hydride gas (for example, H ₂ O, NH ₃ , hydrocarbon gas, BH ₃ , PH ₃ , AsH ₃ , H ₂ Sb, H ₂ S, H ₂ Se, H ₂ Te, etc.),
(B) Diatomic molecular gas (for example, O ₂ , N _2, etc.)
and so on. In order to grow a single crystal with a high yield by using high-speed growth or the metal source 50, it is preferable to use a highly reactive hydride gas as a reactive gas.

[3.3. Carrier gas (or dilution gas)]
In the present invention, the type of carrier gas is not particularly limited, and an optimal one can be selected according to the purpose. Examples of the carrier gas include N ₂ , Ar, H ₂ , He, Ne, and the like. These gases can be used as a carrier gas (or dilution gas) for both the metal-containing gas and the reactive gas.
Further, in addition to the reaction gas and the carrier gas, an organometallic compound gas or the like may be used as appropriate as an impurity addition gas.

[3.4. Seed crystal]
The material of the seed crystal 22 is not particularly limited, and an optimum material is selected according to the composition of the single crystal 32. For example, when growing a GaN single crystal, a sapphire substrate is usually used for the seed crystal 22. The seed crystal 22 is preferably washed to remove impurities and the like before crystal growth. Examples of cleaning methods include carros cleaning, RCA cleaning, and organic cleaning.

[3.5. Formula (10): Temperature control]
In the present embodiment, the growth of the single crystal 32 is performed under the condition that the temperature of each part satisfies the following formula (10).
T _G <T _D <T _S <T _B (10)
However,
_TG is the growth temperature,
T _S is the temperature of the metal source,
T _D is the decomposition temperature of the inorganic compound,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the crucible.
Here, the “growth temperature T _G ” refers to the most advanced temperature of growth, that is, the temperature of the seed crystal 22 or the susceptor 24 in the early stage of growth, and the temperature near the tip of the grown crystal in the middle to late stages of growth. Say.

Expression (10) represents conditions for smoothly generating a metal-containing gas from the crucible 42 and conditions for stably growing the single crystal 32 on the surface of the seed crystal 22.
If the growth temperature _TG is too high, the single crystal 32 grown on the surface of the seed crystal 22 may be decomposed. In order to suppress decomposition of the grown crystal on the surface of the seed crystal 22, it is necessary that T _G <T _D.
If the growth temperature _TG is too low, the surface roughness of the single crystal 32 may occur. In order to suppress surface roughness, T _G ≧ 0.85T _D is preferable.

Further, if the temperature T _S of the metal source 50 is too low, an inorganic compound may be generated in the crucible 42. When an inorganic compound is generated in the crucible 42, a bumping phenomenon, formation of a passive film, etc. may occur, and the supply of the metal-containing gas may become unstable. In order to suppress the formation of unintended inorganic compounds in the crucible 42, it is necessary that T _D <T _S.
Further, the temperature T _B of the porous baffle plate 48 is too low, the metal is liquefied or solidified in the perforated baffle plate 48 surface, causing particles mixed into the growing crystal. In order to suppress liquefaction or solidification of the metal on the surface of the porous baffle plate 48, it is necessary that T _S <T _B.
If the temperature T _S of the metal source 50 is too high, the growth rate of the single crystal 32 may become extremely slow. In order to maintain a high growth rate, T _S ≦ 1.12T _D is preferable.

[3.6. Crucible outlet gas flow rate]
In the present invention, the metal source 50 is isolated from the reaction gas by providing the porous baffle plate 48 at the opening of the crucible 42. Further, the inside of the crucible 42 is purged with the carrier gas, thereby suppressing the reaction gas from being mixed into the crucible 42. In order to suppress the mixing of the reaction gas into the crucible 42, the faster the mixed gas flow rate (crucible outlet gas flow rate) when passing through the porous baffle plate 48, the better.

Here, the crucible outlet gas flow velocity (V _B ) refers to a value represented by the following equation (5).
V _B = (T _B / 300) × Q × (P ₀ / P) × (1 / S _p ) (5)
However,
T _B is the temperature (K) of the perforated baffle plate,
Q is the carrier gas flow rate (m ³ / sec),
P ₀ is atmospheric pressure (101.325 kPa),
P is the process pressure (kPa),
S _p is the opening area (m ² ) of the porous baffle plate.

If V _B is too slow, the reaction gas flows back into the crucible 42 by gas phase diffusion, and the reaction gas directly reacts with the surface of the metal source 50. As a result, a passive film is formed on the surface of the metal source 50, or a bumping phenomenon occurs due to a rapid reaction, so that the supply of the metal-containing gas becomes unstable. In order to suppress the mixing of the reaction gas into the crucible 42, V _B is preferably as large as possible.

Also, by increasing V _B (less than a few m / sec in normal CVD), the time until the metal-containing gas reaches the growth surface is shortened. Therefore, it is possible to suppress the metal-containing gas and the reactive gas from reacting in the gas phase to produce a compound powder, or to suppress the metal-containing gas from condensing as droplets in the gas phase. Thereby, mixing of particles (different orientation crystals, droplets) into the grown crystal can be suppressed, and the crystal quality can be improved.

On the other hand, as V _B increases, the temperature of the porous baffle plate 48 tends to decrease. When the temperature of the perforated baffle plate 48 is lowered, the temperature of the metal-containing gas passing through the perforated baffle plate 48 is lowered. As a result, a metal liquid film may be formed on the surface of the grown crystal. Further, when the temperature of the porous baffle plate 48 is low, when the reaction gas passes through the porous baffle plate 48, the reaction gas is mixed into the crucible 42 without being decomposed. As a result, the reaction gas and the metal source 50 may react vigorously in the crucible 42.
On the other hand, when the perforated baffle plate 48 that satisfies the above-described conditions is used, even if the V _B is relatively low, the high growth rate, the prevention of the formation of a liquid film on the growth crystal surface, and the reaction gas inside the crucible 42 are obtained. It is possible to achieve prevention of contamination at the same time. Specifically, even when V _B is in the range of 1 m / sec or more and less than 20 m / sec, the above problem can be solved.

[3.7. Growth pressure and baffle-growth crystal distance]
Improving the raw material yield is very important from the viewpoint of cost reduction. The present inventors have found that the growth pressure P and the baffle-growth crystal distance D are important parameters that affect the raw material yield.
Here, the “raw material yield” refers to the ratio of the weight of the metal source 50 taken into the growth crystal to the weight of the evaporated metal source 50.

In order to obtain a high raw material yield, it is preferable to grow the single crystal so that the growth pressure P satisfies the formula (6) and the baffle-grown crystal distance D satisfies the formula (7). When P and D exceed this range, the raw material yield is significantly reduced. On the other hand, when P and D are below this range, it is difficult to control growth parameters such as pressure.
0.1 kPa <P <6 kPa (6)
0.5 cm ≦ D <5 cm (7)

[3.8. Growth rate]
When the compound single crystal manufacturing apparatus according to the present invention is used, a crystal growth rate of ˜100 μm / h can be easily realized. From the viewpoint of manufacturing cost, the growth rate is desirably 200 μm / h or more.
On the other hand, when the growth rate is too fast, polycrystallization and growth of crystal defects occur, and crystal quality deteriorates. Therefore, the growth rate is preferably 2 mm / h or less.

[3.9. Growth crystal size]
When the compound single crystal manufacturing apparatus according to the present invention is used, a single crystal having a growth height of several centimeters and a crystal diameter (diameter) of several inches (tens of centimeters) is obtained. From the viewpoint of manufacturing costs (including cutting costs), the growth height is preferably 20 mm or more. Further, from the viewpoint of device cost, the crystal diameter is desirably 50 mm or more.

[4. Method for producing compound single crystal (2)]
The method for producing a compound single crystal according to the second embodiment of the present invention uses a compound single crystal production apparatus 12 according to the second embodiment of the present invention, under a predetermined temperature condition, and a seed crystal 22. A single crystal 32 made of an inorganic compound is grown on the surface of the substrate.

[4.1. Metal source]
As described above, when the crucible (laminated crucible) 72 is used, each k-th crucible 72 (k) may be filled with the same type of metal source or with a different type of metal source. However, since the carrier gas flows from the first crucible 72 (1) at the bottom to the nth crucible 72 (2) at the top, a metal source that hardly generates metal-containing gas is generated in the crucible at the bottom. When filled, the metal-containing gas may be liquefied or solidified in the upper crucible.

Therefore, it is preferable to fill the lower crucible with a metal source that is easily vaporized and fill the upper crucible with a metal source that is difficult to vaporize.
For example, in the case where each of the kth metal sources 72 (k) (1 ≦ k ≦ n) is made of only metal, in order to generate a predetermined amount of metal vapor from each kth crucible 72 (k), The boiling point of the k + 1) metal source 72 (k + 1) is preferably equal to or higher than the boiling point of the kth metal source 72 (k).
Other points regarding the metal source are the same as those in the first embodiment, and thus the description thereof is omitted.

[4.2. Formula (11) and Formula (12): Temperature Control]
In the present embodiment, the growth of the single crystal 32 is performed under the condition that the temperature of each part satisfies the following expressions (11) and (12).
T _G <T _D ≦ T _Dmax <T _Sn <T _B (11)
T _Sk ≦ T _{Sk + 1} (1 ≦ k ≦ n−1) (12)
However,
T _G is the growth temperature,
T _Sn is the temperature of the nth metal source filled in the nth crucible,
T _D is the decomposition temperature of the first inorganic compound,
_TDmax is the maximum value of the decomposition temperature of the inorganic compound produced from any one or more metal elements contained in the first metal source to the nth metal source and the reaction gas,
T _Sk is the temperature of the kth metal source charged in the kth crucible,
T _{Sk + 1} is the temperature of the (k + 1) th metal source filled in the (k + 1) crucible,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the n-th crucible.

Expression (11) represents conditions for smoothly generating a metal-containing gas from the crucible 72 and conditions for stably growing the single crystal 32 on the surface of the seed crystal 22. In formula (11), T _Dmax <T _Sn is for suppressing the formation of an unintended inorganic compound (not necessarily the same as the inorganic compound constituting the single crystal 32) in the nth crucible 72 (n). Represents the condition. About another point, it has the same meaning as Formula (10).
Equation (12) represents a condition for smoothly generating a metal-containing gas from each of the plurality of k-th crucibles 72 (k). The carrier gas flows from the first crucible 72 (1) toward the nth crucible 72 (n). Therefore, if the temperature of the (k + 1) th crucible 72 (k + 1) on the downstream side is lower than the temperature of the kth crucible 72 (k) on the upstream side, the metal-containing gas generated on the upstream side may be liquefied or solidified. There is. Therefore, it is necessary that T _Sk ≦ T _{Sk + 1} .

[4.3. Other configurations]
Other points regarding the method for producing the compound single crystal according to the second embodiment are the same as those in the first embodiment, and thus the description thereof is omitted.

[5. Suitable growth conditions]
A nitride single crystal is known as a representative compound that is difficult to grow a single crystal. Hereinafter, detailed growth conditions for growing a nitride single crystal using the present invention will be described.

[5.1. Suitable growth conditions for GaN single crystal]
[5.1.1. material]
In order to grow a GaN single crystal, it is preferable to use metal Ga as the metal source and NH ₃ as the reaction gas. The carrier gas (dilution gas) for transporting the metal vapor and the reaction gas is preferably an inert gas such as N ₂ or Ar.
GaN or Ga ₂ O ₃ can also be used as the metal source. However, GaN decomposes with the passage of growth time, changes the evaporation rate, and the supply becomes unstable. In addition, when Ga ₂ O ₃ is used, oxygen impurities in the grown crystal increase, which is not suitable for high purity. However, when oxygen is intentionally doped, an appropriate amount (1 to 20 mass%) of Ga ₂ O ₃ can be added to the metal Ga.

[5.1.2. Metal source temperature]
The temperature T _{S of the} metal Ga is preferably 1200 ° C. <T _S <1350 ° C.
The temperature (decomposition temperature T _D ) at which the decomposition of GaN becomes remarkably remarkable is ˜1200 ° C. Therefore, if the temperature T _{S of the} metal Ga is equal to or lower than the decomposition temperature T _D , the reaction gas mixed in a small amount in the crucible reacts with the metal Ga, and a passive film (film with a low evaporation rate) is formed on the surface of the metal Ga. Formed and the growth rate is reduced. Therefore, the temperature T _{S of the} metal Ga is preferably T _S > 1200 ° C.
On the other hand, when the temperature T _S of the metal Ga is too high, when the reaction with the mixed gas passing through the perforated baffle plate (a metal vapor + carrier gas) gas is joined, decomposed too is acceleration of the reaction gases, on the growth surface The substantial reaction gas partial pressure is too low. Therefore, the temperature T _{S of the} metal Ga is preferably T _S <1350 ° C.

[5.1.3. Growth temperature]
The growth temperature T _G is preferably 1000 ° C. <T _G <1200 ° C.
If the growth temperature (the temperature of the seed crystal surface or the growth crystal surface) _TG is too low, the crystal quality is deteriorated. Therefore, the growth temperature T _G is preferably T _G > 1000 ° C.
On the other hand, if the growth temperature _TG is too high, the GaN crystal is decomposed on the growth crystal surface, and a Ga liquid film is formed. Therefore, T _G is preferably T _G <1200 ° C.

[5.1.4. Perforated baffle plate temperature]
Temperature T _B of the porous baffle plate, it is essential to exceed the temperature T _S of the metal source. The temperature T _B of the porous baffle plate is particularly preferably T _B ≧ T _S + 50 ° C. The temperature T _B of the porous baffle plate With such a range, it is possible to Ga droplets or polycrystalline GaN is completely prevented from adhering to the porous baffle plate.

[5.2. Suitable growth conditions for InN single crystal]
[5.2.1. material]
In order to grow an InN single crystal, it is preferable to use metal In as a metal source and NH ₃ as a reaction gas. The carrier gas (dilution gas) for transporting the metal vapor and the reaction gas is preferably an inert gas such as N ₂ or Ar.
InN or In ₂ O ₃ can also be used as the metal source. However, InN decomposes as the growth time elapses and the evaporation rate changes, and the supply becomes unstable. In addition, if In ₂ O ₃ is used, oxygen impurities in the grown crystal increase, which is not suitable for high purity. However, when oxygen is intentionally doped, an appropriate amount (1 to 20 mass%) of In ₂ O ₃ can be added to the metal In.

[5.2.2. Metal source temperature]
The temperature T _{S of the} metal In is preferably 800 ° C. <T _S <1000 ° C.
The temperature (decomposition temperature T _D ) at which the decomposition of InN becomes remarkably remarkable is 800 ° C. Therefore, when the temperature T _{S of the} metal In is equal to or lower than the decomposition temperature T _D , the reaction gas mixed in a small amount in the crucible reacts with the metal In, and a passive film (film with a low evaporation rate) is formed on the surface of the metal In. Formed and the growth rate is reduced. Therefore, the temperature T _{S of the} metal In is preferably T _S > 800 ° C.
On the other hand, when the temperature T _S of the metal In is too high, the gas mixture passing through the perforated baffle plate (a metal vapor + carrier gas) to raise the surface temperature of the growing crystal, that the surface temperature deviates from the appropriate temperature range is there. Therefore, the temperature T _{S of the} metal In is preferably T _S <1000 ° C.

[5.2.3. Growth temperature]
The growth temperature T _G is preferably 700 ° C. <T _G <800 ° C.
If the growth temperature (the temperature of the seed crystal surface or the growth crystal surface) _TG is too low, the crystal quality is deteriorated. Therefore, the growth temperature T _G is preferably T _G > 700 ° C.
On the other hand, if the growth temperature _TG is too high, the InN crystal is decomposed on the surface of the growth crystal, and an In liquid film is formed. Therefore, T _G is preferably T _G <800 ° C.

[5.2.4. Perforated baffle plate temperature]
Temperature T _B of the porous baffle plate, it is essential to exceed the temperature T _S of the metal source. The temperature T _B of the porous baffle plate is particularly preferably T _B ≧ T _S + 50 ° C. The temperature T _B of the porous baffle plate With such a range, it is possible In the droplet and InN polycrystalline completely prevented from adhering to the porous baffle plate.

[5.3. Suitable growth conditions for AlN single crystal]
[5.3.1. material]
In order to grow an AlN single crystal, it is preferable to use metal Al as the metal source and NH ₃ and N ₂ as the reaction gas. A carrier gas (dilution gas) for transporting the metal vapor and the reaction gas is preferably a rare gas such as Ar.
AlN or Al ₂ O ₃ can also be used as the metal source. However, these have a low evaporation rate and are not suitable for high-speed growth.

[5.3.2. Metal source temperature]
The temperature T _{S of the} metal Al is preferably 1500 ° C. <T _S <1800 ° C.
The temperature (decomposition temperature T _D ) at which the decomposition of AlN becomes remarkably remarkable is 1500 to 1520 ° C. Therefore, if the temperature T _{S of the} metal Al is below the decomposition temperature T _D , the reaction gas mixed in a small amount in the crucible reacts with the metal Al, and a passive film (film with a low evaporation rate) is formed on the surface of the metal Al. Formed and the growth rate is reduced. Therefore, the temperature T _{S of the} metal Al is preferably T _S > 1500 ° C.
On the other hand, if the temperature T _{S of the} metal Al is too high, the furnace structure material (quartz chamber or the like) is damaged by radiant heat. Therefore, the temperature T _{S of the} metal Al is preferably T _S <1800 ° C.

[5.3.3. Growth temperature]
The growth temperature T _G is preferably 1300 ° C. <T _G <1800 ° C.
If the growth temperature (the temperature of the seed crystal surface or the growth crystal surface) _TG is too low, the crystal quality is deteriorated. Therefore, the growth temperature T _G is preferably T _G > 1300 ° C.
On the other hand, if the growth temperature _TG is too high, the growth rate decreases. Therefore, T _G is preferably T _G <1800 ° C.

[5.3.4. Perforated baffle plate temperature]
Temperature T _B of the porous baffle plate, it is essential to exceed the temperature T _S of the metal source. The temperature T _B of the porous baffle plate is particularly preferably T _B ≧ T _S + 50 ° C. The temperature T _B of the porous baffle plate With such a range, it is possible to Al droplets or polycrystalline AlN is completely prevented from adhering to the porous baffle plate.

[5.4. Suitable growth conditions for InGaN single crystal]
[5.4.1. material]
When growing an InGaN single crystal, a laminated crucible is used as the crucible. Further, it is preferable to use metal In as the first metal source, use metal Ga as the second metal source, and use NH ₃ as the reaction gas. The carrier gas (dilution gas) for transporting the metal vapor and the reaction gas is preferably an inert gas such as N ₂ or Ar.

[5.4.2. Metal source temperature]
The temperature T _{S1 of the} metal In is [5.2.2. ], The reason is preferably 800 ° C. <T _S1 <1000 ° C.
The temperature T _{S2 of the} metal Ga is preferably 1200 ° C. <T _S2 <1350 ° C.
GaN decomposition is significantly significantly temperature (decomposition temperature T _D2) is 1200 ° C., higher than the decomposition temperature T _D of the decomposition temperature T _D1 and InGaN of InN. Therefore, when the temperature T _{S2 of the} metal Ga is equal to or lower than the decomposition temperature T _D2 , the reaction gas mixed in a small amount in the crucible reacts with the metal Ga, and a passive film (film with a low evaporation rate) is formed on the surface of the metal Ga. It will form and the growth rate will decrease. Therefore, the temperature T _{S2 of the} metal Ga is preferably T _S2 > 1200 ° C.
On the other hand, if the temperature T _{S2 of the} metal Ga is too high, when the mixed gas (metal vapor + carrier gas) that has passed through the porous baffle plate and the reactive gas merge, the decomposition of the reactive gas is promoted too much, and The substantial reaction gas partial pressure is too low. Therefore, the temperature T _{S2 of the} metal Ga is preferably T _S2 <1350 ° C.

[5.4.3. Growth temperature]
The growth temperature T _G is preferably 700 ° C. <T _G <1200 ° C.
If the growth temperature (the temperature of the seed crystal surface or the growth crystal surface) _TG is too low, the crystal quality is deteriorated. Therefore, the growth temperature T _G is preferably T _G > 700 ° C.
On the other hand, if the growth temperature _TG is too high, the crystal is decomposed. Therefore, T _G is preferably T _G <1200 ° C.

[5.5. Suitable growth conditions for AlGaN single crystal]
[5.5.1. material]
When growing an AlGaN single crystal, a laminated crucible is used as the crucible. It is also preferable to use metal Ga as the first metal source, metal Al as the second metal source, and NH ₃ and N ₂ as the reaction gas. A carrier gas (dilution gas) for transporting the metal vapor and the reaction gas is preferably a rare gas such as Ar.

[5.5.2. Metal source temperature]
The temperature T _{S1 of the} metal Ga is [5.1.2. ] For the same reason as above, 1200 ° C. <T _S1 <1350 ° C. is preferable.
The temperature T _{S2 of the} metal Al is preferably 1500 ° C. <T _S2 <1800 ° C.
Temperature at which the decomposition of AlN is markedly significantly (decomposition temperature T _D2) is 1500 ° C., higher than the decomposition temperature T _D of GaN decomposition temperature T _D1 and AlGaN. Therefore, when the temperature T _{S2 of the} metal Al is lower than the decomposition temperature T _D2 , the reaction gas mixed in a small amount in the crucible reacts with the metal Al, and a passive film (film with a low evaporation rate) is formed on the surface of the metal Al. It will form and the growth rate will decrease. Therefore, the temperature T _{S2 of the} metal Al is preferably T _S2 > 1500 ° C.
On the other hand, if the temperature T _{S2 of the} metal Al is too high, the furnace structure material (quartz chamber or the like) is damaged by radiant heat. Therefore, the temperature T _{S2 of the} metal Al is preferably T _S <1800 ° C.

[5.5.3. Growth temperature]
The growth temperature T _G is preferably 1000 ° C. <T _G <1500 ° C.
If the growth temperature (the temperature of the seed crystal surface or the growth crystal surface) _TG is too low, the crystal quality is deteriorated. Therefore, the growth temperature T _G is preferably T _G > 1000 ° C.
On the other hand, if the growth temperature _TG is too high, the crystal is decomposed. Therefore, T _G is preferably T _G <1500 ° C.

[5.6. NH ₃ partial pressure]
When NH ₃ is used as a reaction gas when growing a nitride single crystal, the partial pressure P _NH3 of NH _{3 in} the growth atmosphere is preferably 0.1 kPa <P _NH3 <1 kPa.
When the partial pressure P _NH3 of NH ₃ is too low, the metal-containing gas to form a condensed liquid film on the growing crystal surface. Therefore, P _NH3 is preferably P _NH3 > 0.1 kPa.
On the other hand, when the P _NH3 is too high, it reacts with the metal-containing gas and NH ₃ in the gas phase is likely to produce a nitride powder is increased. Nitride powder generated in the gas phase can cause particle contamination in the grown crystal. Therefore, P _NH3 is preferably P _NH3 <1 kPa.

[6. GaN single crystal]
The GaN single crystal according to the present invention has a C impurity amount of less than 8 × 10 ¹⁵ cm ⁻³ , an H impurity amount of less than 3 × 10 ¹⁶ cm ⁻³ , and an O impurity amount of 6 × 10 ¹⁵ cm 3. Less than ^-3 . Here, “impurity” refers to a value measured using secondary ion mass spectrometry.
As described above, when the GaN single crystal is grown using the apparatus according to the present invention, if the perforated baffle plate 48 and the crucible 42 are optimized, a single crystal having a higher quality than the conventional one can be grown. Can grow at speed. this is,
(A) By optimizing the structure of the porous baffle plate 48, the temperature reduction of the porous baffle plate 48 can be suppressed without reducing the growth rate; and
(B) By optimizing the material of the crucible 42, the creeping of the liquid Ga to the wall surface of the crucible during crystal growth is suppressed.
it is conceivable that.

[7. Action]
In general, in order to obtain a bulk nitride single crystal (growth height: -10 mm or less), HVPE (Hydride Vapor Phase Epitaxy) method is used (see FIG. 5). The HVPE method can easily achieve a growth rate of about 100 μm / h. However, HCl gas is used to transport group III elements, and ammonia is used as a raw material for group IV elements, so ammonium chloride is generated as a by-product. Ammonium chloride causes the exhaust pipe to become clogged. Therefore, the HVPE method is not suitable for long-time growth.

In the sublimation method, GaN crystals are grown using metal Ga or GaN powder as a raw material and NH ₃ as a reaction gas (see FIG. 6). In the sublimation method, there is a report that high-speed growth similar to that in the HVPE method is possible, but there is no report that a large crystal having a thickness exceeding 1 mm is obtained.
This is because when only GaN is used as a raw material, the supply of the raw material is interrupted during the growth because GaN is decomposed and denatured into metal Ga as the growth time elapses.

In addition, when metal Ga is used as a raw material in the sublimation method, Ga overflows from the crucible during growth, and the entire apparatus is covered with Ga. The reason why Ga overflows is that GaN is deposited on the surface of the crucible holding metal Ga. Molten Ga wets very well with GaN, so when GaN precipitates on the crucible surface, the molten Ga creeps up easily. For this reason, there is no example in which long-term growth of 2 hours or more is stably realized using metal Ga.
Furthermore, although the yield of Ga in these methods has not been reported, it is considered to be very small (about 15%).

  On the other hand, a method using gallium hydride generated by the reaction of metal Ga and hydrogen as a precursor is also known. However, since the GaN crystal is etched by hydrogen, the growth rate is limited to less than 100 μm / h.

Furthermore, in order to achieve good crystal growth using the sublimation method, the metal vapor or the sublimation gas reaches the growth surface in an atomic or molecular form, and the metal vapor or the sublimation gas and the reaction gas on the growth surface. It is necessary to react. However, it is generally difficult to stably grow a bulk single crystal by such a method. this is,
(A) generating a compound powder in the gas phase by a gas phase reaction;
(B) the metal liquefies or solidifies in the gas phase, on the surface of the grown crystal, or on other structural members;
(C) Since the reactive gas reacts directly with the metal source in the crucible and forms a passive film on the surface of the metal source, or a sudden reaction occurs due to a sudden reaction, the supply of metal vapor or sublimation gas Becoming unstable,
This is considered to be the main cause.

On the other hand, when crystal growth is performed using the sublimation method, when a porous baffle plate is provided in the opening of the crucible filled with the metal source and a carrier gas is flowed into the crucible, the mixed gas is discharged from the crucible. At the same time, the backflow of the reaction gas into the crucible is suppressed. For this reason, the supply of the metal-containing gas is stabilized.
Further, in the case of growing a single crystal, when the temperature of each part is optimized, generation of compound powder in the gas phase and liquefaction or solidification of metal at an unintended site can be suppressed. Therefore, it is possible to reduce the manufacturing cost of the compound single crystal and increase the crystal size.

  Furthermore, if the shape of the porous baffle plate is optimized, crystals can be stably grown even when the outlet gas flow rate is less than 20 m / sec. Further, when the relative density or average pore diameter of the crucible is optimized, the liquid metal can be prevented from scooping up the crucible wall surface when the liquid metal is used as the metal source. When such an apparatus is used, a GaN single crystal having an extremely low concentration of C, H, and O impurities can be obtained.

(Example 1: Crawling height)
[1. Test method]
Using a crucible having an average pore diameter of about 10 μm, the rising height of the liquid Ga was measured. Moreover, the creeping height (h) was calculated using Formula (4).
[2. result]
FIG. 7 shows the average pore diameter dependence of the Ga creeping height. FIG. 7 shows that the average pore diameter should be 100 μm or more in order to make the creeping height (h) be several cm or less.

(Examples 2-4, Comparative Examples 1-2: Volume ratio)
[1. Preparation of sample]
A GaN single crystal was grown using the compound single crystal growth apparatus shown in FIG. Metal Ga was used as the metal source, and NH ₃ was used as the reaction gas. A sapphire template with a MOCVD-GaN film (thickness 2 μm) having a diameter of 2 inches (5.08 cm) was used as a seed crystal. N ₂ was used as a carrier gas for transporting Ga vapor and a diluent gas (carrier gas) for NH ₃ , respectively. The porous baffle plate 48 having a diameter of 15 mm (Comparative Example 1), 20 mm (Comparative Example 2), 30 mm (Example 2), 40 mm (Example 3), or 50 mm (Example 4) was used. . Each perforated baffle plate 48 was formed with 45 holes each having a cylindrical shape with a diameter of 2 mm and a length of 4 mm. Growth conditions were adjusted so that the crucible outlet gas flow rate was 0.9 m / sec, and growth was performed for 1 h.

[2. Test method and results]
The surface state of the obtained GaN single crystal was visually evaluated. Moreover, the particle mixing density in the grown crystal was measured using an optical microscope. Table 1 shows the results. FIG. 8 shows the relationship between the diameter of the porous baffle plate and the volume ratio (1-V _H / V _B ) × 100.

From the results of visual observation, it was found that no Ga droplets existed on the surfaces of the GaN growth crystals of Examples 2 to 4, a smooth mirror surface was exhibited, and good crystal quality was achieved. On the other hand, Ga droplets were generated on the surfaces of the grown crystals of Comparative Examples 1 and 2. this is,
(A) When the temperature of Ga vapor dropped when passing through the porous baffle plate 48, Ga droplets were formed, and (b) liquid Ga caused bumping due to mixing of NH ₃ gas into the crucible 42,
it is conceivable that.
When the volume ratio is small, the heat capacity of the porous baffle plate 48 is small. Therefore, it is considered that Ga vapor cooling occurs due to the temperature drop of the porous baffle plate 48 due to the gas. Further, since the temperature of the porous baffle plate 48 is low, it is considered that the NH ₃ gas passes through the porous baffle plate 48 without being decomposed and reaches the liquid Ga in the crucible 42. From the above results, it was found that the volume ratio of the porous baffle plate 48 is preferably 80% or more.

(Examples 5 to 9: Crucible outlet gas flow rate dependence)
[1. Preparation of sample]
A GaN single crystal was produced in the same manner as in Example 2 except that the crucible outlet gas flow rate was 0.3 to 15 m / sec. A porous baffle plate 48 having a diameter of 40 mm, a hole size of 2 mm in diameter × 4 mm in length, a number of holes of 45, and a volume ratio of 88.75% was used.

[2. Test method and results]
The surface state of the obtained GaN single crystal was visually evaluated. Moreover, the growth rate of each single crystal was calculated. Table 2 shows the results. FIG. 9 shows the dependence of the GaN growth rate on the carrier gas flow rate.

Under all conditions, mixing of NH ₃ into the crucible 42 was not confirmed. However, as the crucible outlet gas flow rate decreased, the amount of Ga vapor supplied also decreased. When the crucible outlet gas flow rate was less than 1 m / sec, the growth rate was less than 100 μm / h. Considering the production efficiency, the growth rate is preferably 100 μm / h or more. From the above results, it was found that the crucible outlet gas flow rate is preferably 1 m / sec or more.

(Example 10: a ² / L ratio)
[1. Test method]
Porous baffle plates 48 having different a ² / L ratios were produced, and the relationship between the a ² / L ratio and the crucible outlet gas flow rate was examined. The temperature of the perforated baffle plate 48 was 1300 ° C., and the process pressure was 4 kPa.

[2. result]
FIG. 10 shows the a ² / L dependency of the crucible outlet gas flow rate. 10 that the crucible outlet gas flow velocity is 1 m / sec or more when the a ² / L ratio of the porous baffle plate 48 is in the range of 0.00033 <a ² /L<1.1.

(Example 11: S _B / S _L ratio)
[1. Test method]
GaN single crystals were grown under different conditions of S _B / S _L ratio. The conditions other than the S _B / S _L ratio were the same as in Example 2.

[2. result]
FIG. 11 shows the dependency of the normalized growth rate on the S _B / S _L ratio. Here, the “normalized growth rate” refers to a value obtained by normalizing the growth rate under each condition with the growth rate when S _B / S _L = 1. From FIG. 11, it can be seen that when the S _B / S _L ratio is less than 0.1, the normalized growth rate rapidly decreases and is less than 0.05. From the above results, it was found that the S _B / S _L ratio is preferably 0.1 or more.

(Example 12, Comparative Example 3: GaN single crystal)
[1. Preparation of sample]
A GaN single crystal was grown under the same conditions as in Example 9 (Example 12).
For comparison, a GaN single crystal was grown under conditions (73.8 m / sec) at which the outlet carrier gas flow rate was faster than that in Example 9 (Comparative Example 3).

[2. Test method and results]
Impurities contained in the GaN single crystal were measured by secondary ion mass spectrometry. Table 3 shows the results. As shown in Table 3, C, H, and O impurities are C <8 × 10 ¹⁵ cm ⁻³ (below the background level), H <3 × 10 ¹⁵ cm ⁻³ (below the background level), and O <6 × 10 ¹⁵ cm ⁻³ (below the background level).
Thus, a GaN single crystal in which all of the C, H, and O impurities are below the background level has not been obtained by the conventionally used HVPE method or MOCVD method. This is because, according to the present invention, it is possible to suppress the creeping up of Ga and suppress the incorporation of impurities into the raw material Ga, or by lowering the outlet carrier gas flow velocity, C, H, This is probably because the O impurity concentration was greatly reduced.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  The compound single crystal production apparatus according to the present invention can be used as an apparatus for producing nitride single crystals such as GaN, InN, AlN, InGaN, and AlGaN.

DESCRIPTION OF SYMBOLS 10 Compound single crystal manufacturing apparatus 20 Crystal growth part 22 Seed crystal 24 Susceptor 40 Gas supply part 42 Crucible 48 Porous baffle plate 50 Metal source 60 Heating part 62 Heating apparatus

Claims (18)

A GaN single crystal having a C impurity amount of less than 8 × 10 ¹⁵ cm ⁻³ , a H impurity amount of less than 3 × 10 ¹⁶ cm ⁻³ , and an O impurity amount of less than 6 × 10 ¹⁵ cm ⁻³ . Compound single crystal production apparatus having the following configuration.
(1) The compound single crystal production apparatus comprises:
A crystal growth section having a susceptor for holding a seed crystal;
A gas supply unit for supplying a metal-containing gas (a gas containing a metal vapor) generated from a metal source and a reaction gas that reacts with the gas to generate an inorganic compound toward the seed crystal;
A heating unit including a heating device for heating the seed crystal and the metal source.
(2) The gas supply unit
A crucible for holding the metal source, spaced apart from the susceptor;
A carrier gas supply device for supplying a carrier gas into the crucible and supplying a mixed gas of the metal-containing gas and the carrier gas toward the seed crystal;
A reaction gas supply device for supplying the reaction gas toward the seed crystal;
It has.
(3) A porous baffle plate is provided at the opening of the crucible.
(4) The porous baffle plate satisfies the relationship of the following formulas (1) and (2).
80% ≦ (1-V _H / V _B ) × 100 <100% (1)
0.0003 <a ² /L<1.1 (2)
However,
V _B is the apparent volume of the perforated baffle plate,
V _H is the total volume of holes contained in the perforated baffle plate.
a is the diameter of the hole,
L is the length of the hole.   The compound single crystal manufacturing apparatus according to claim 2, wherein the hole has a portion having a different diameter along a thickness direction of the porous baffle plate. The ratio (= S _B / S _L ) of the area (S _B ) of the perforated baffle plate to the surface area (S _L ) of the metal source held by the crucible is 0.1 or more. The compound single crystal manufacturing apparatus of description.   5. The compound single crystal production apparatus according to claim 2, wherein the crucible is made of a material having a relative density of 99% or more or a material having an average pore diameter of 100 μm or more. A first movable device for changing a vertical distance or a horizontal distance between the perforated baffle plate and the susceptor, and / or
The compound single crystal manufacturing apparatus according to any one of claims 2 to 5, further comprising a second movable device for changing a vertical distance or a horizontal distance between the heating device and the crucible. The susceptor is disposed above the crucible;
The first movable device is capable of moving the susceptor in a vertical direction;
The compound single crystal manufacturing apparatus according to claim 6, wherein the second movable device is capable of moving the heating device in a vertical direction. The crucible is
(A) an inner crucible for holding the metal source, and an outer crucible for accommodating the inner crucible,
(B) Between the outer wall surface of the inner crucible and the inner wall surface of the outer crucible, a carrier gas flow path is provided for flowing a carrier gas toward the inside of the inner crucible.
(C) The carrier gas introduction hole for introducing the carrier gas into the carrier gas flow path is provided on a bottom surface or a side surface of the outer crucible, according to any one of claims 2 to 7. Compound single crystal production equipment. The carrier gas flow path is configured to allow the carrier gas to flow toward the tip of the inner crucible,
The carrier gas flow direction adjuster for changing the flow of the carrier gas that has reached the tip of the inner crucible to a direction toward the metal source is provided at an upper portion of the outer crucible. Compound single crystal production equipment. The gas supply unit includes a reactive gas flow direction adjuster provided between the susceptor and the crucible,
10. The reactive gas flow direction adjuster is configured to change the flow direction of the reactive gas to a direction toward the mixed gas and promote mixing of the mixed gas and the reactive gas. The compound single crystal manufacturing apparatus according to any one of the preceding items.   The compound single crystal manufacturing apparatus according to any one of claims 2 to 10, further comprising an angle changing device that changes a tilt angle of the surface of the seed crystal. The crucible is a laminated crucible stacked in the order of the first crucible, the second crucible, the nth crucible (n ≧ 2) from the bottom to the top, and the kth crucible (1 ≦ k ≦ n−1). And the carrier gas introduction hole of the (k + 1) th crucible is connected,
The compound single crystal manufacturing apparatus according to any one of claims 8 to 11, wherein the perforated baffle plate is provided at least in an opening of the n-th crucible located at the uppermost part. Using the compound single crystal manufacturing apparatus according to any one of claims 2 to 11, the surface of the seed crystal is made of the inorganic compound under the condition that the temperature of each part satisfies the following formula (10). A method for producing a compound single crystal for growing a single crystal.
T _G <T _D <T _S <T _B (10)
However,
_TG is the growth temperature,
T _S is the temperature of the metal source,
T _D is the decomposition temperature of the inorganic compound,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the crucible. Using the compound single crystal manufacturing apparatus according to claim 12, a single crystal made of the inorganic compound is formed on the surface of the seed crystal under the condition that the temperature of each part satisfies the following formulas (11) and (12). A method for producing a compound single crystal to be grown.
T _G <T _D ≦ T _Dmax <T _Sn <T _B (11)
T _Sk ≦ T _{Sk + 1} (1 ≦ k ≦ n−1) (12)
However,
_TG is the growth temperature,
T _Sn is the temperature of the nth metal source filled in the nth crucible,
T _D is the decomposition temperature of the inorganic compound,
_TDmax is the maximum value of the decomposition temperature of the inorganic compound produced from any one or more metal elements contained in the first metal source to the nth metal source and the reaction gas,
T _Sk is the temperature of the kth metal source filled in the kth crucible,
T _{Sk + 1} is the temperature of the (k + 1) th metal source filled in the (k + 1) crucible,
T _B is the temperature of the apertured baffle plate provided on the opening portion of the n-th crucible. The k-th metal source (1 ≦ k ≦ n) is made of only metal,
The method for producing a compound single crystal according to claim 14, wherein the boiling point of the (k + 1) th metal source is equal to or higher than the boiling point of the kth metal source.   The carrier gas is supplied so that a flow rate of the mixed gas (crucible outlet gas flow rate) when passing through the porous baffle plate is 1 m / sec or more and less than 20 m / sec. A method for producing the compound single crystal according to Item. The single crystal is grown so that the growth pressure P satisfies the expression (3) and the distance D between the porous baffle plate and the surface of the growth crystal satisfies the expression (4). The manufacturing method of the compound single crystal of any one of the above.
0.1 kPa <P <6 kPa (3)
0.5 cm ≦ D <5 cm (4) The metal source is made of a metal containing at least one metal element selected from the group consisting of Al, Ga, In, Zn, Cd, Hg, Si, Ge, Sn, Mg, Mn, Cu, and Ag. ,
18. The reaction gas according to claim 13, wherein the reaction gas comprises a gas containing one or more elements selected from the group consisting of C, B, N, P, As, Sb, O, S, Se, and Te. The manufacturing method of the compound single crystal of any one.

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